Free form fabrication (FFF), direct manufacturing (DM), and additive manufacturing (AM) are names for a general class of layer manufacturing (LM), in which a three-dimensional (3-D) article is made by the sequential build-up of layers of material. One or more suitable LM techniques may be utilized for making articles, (e.g., such as by creating one or more device patterns directly on a substrate). The LM technique usually includes a step of selectively depositing material layer by layer, selectively removing material layer by layer, or a combination thereof. Many LM techniques are attractive in that they avoid the need for masks, for pre-existing three-dimensional patterns, and/or expensive tooling.
As it pertains to making metallic articles by LM, one approach that has gained momentum in recent years has been to employ electron beam energy to heat and melt an advancing supply of a feed material. Efforts to address some of the problems encountered in LM, particularly LM processing that employs electron beam energy and closed loop control methodologies, are described in U.S. Application No. 61/243,242 (incorporated by reference), which discloses various unique approaches to layer manufacturing. In general, these approaches address deposition condition monitoring by use of optical approaches, such as by monitoring with digital camera equipment. Notwithstanding the early success of such a system, there remains a need for other robust approaches to deposition condition monitoring. U.S. Application No. 61/261,090 (incorporated by reference) discloses another approach to monitoring conditions during an LM operation that includes monitoring a molten pool deposit for at least one preselected condition, such as width, by detecting electrons from an emitted beam.
Notwithstanding the success of the above efforts directed at monitoring, there remains a need for improved LM technologies, especially in connection with the ability to manage energy that is emitted (e.g., by an electron beam gun) during an LM operation, so that efficient melting and solidification is possible, with minimal interruption to manufacturing.
By way of background, it has been observed that for successful deposition of a material such as a metal onto a dynamically changing substrate during LM there are at least two competing heat conditions that must be considered. A first condition is the heat to which a feed material is subjected to melt it. A second condition is the heat to which a molten pool resulting from deposition of the feed material, and possibly at least some of the surrounding solidified material, is subjected. In theory, it may be possible to predict the first condition, as it will generally be dictated by factors such as feed rate, specific heat, and melting temperature of the feed material. The second condition, however, is not readily predictable, as it will depend upon the amount of material that is deposited; the amount of material that has solidified (in contrast with that which is in a liquid state); the geometry of the resulting workpiece (inasmuch as that will affect the heat transfer and/or thermal mass characteristics of the workpiece); and other considerations that are continually changing in the course of material deposition. One approach to manage these competing conditions may be to employ a first energy source that melts the feed material, and a second independent energy source that manages the heat delivered to the molten pool, the surrounding solidified material, or both. For example, the use of two or more separate electron beam guns may be employed, one for each purpose.
It has been proposed in U.S. Application No. 61/243,242 (incorporated by reference) and U.S. Application No. 61/261,090 (incorporated by reference) to monitor the molten pool and make adjustments to a processing condition based upon information from such monitoring. For example, it describes monitoring the size (e.g., width) of the molten pool, and based upon information obtained, changing one or more processing conditions in an effort to maintain the molten pool within a predetermined size range.
It would be quite attractive for a LM process, particularly one that employs a closed loop control system, to be able to operate while maintaining, generally constant, as many processing conditions as possible. It would also be attractive to achieve such operation in an LM process with minimal investment in equipment. For example, it would be attractive to have an LM system that only requires the employment of a single electron beam gun.
Examples of efforts to provide layer manufacturing of articles and processes include those disclosed in U.S. Pat. Nos. 5,534,314; 5,669,433; 5,736,073; 5,871,805; 5,960,853; 6,401,001; 6,193,923; 6,405,095; 6,459,951; 6,680,456; 7,073,561; 7,168,935; and 7,326,377; and US Patent Application Nos. 20030075836; 20050173380; and 20050288813, all of which are incorporated by reference for all purposes. The possibility of closed loop controls for additive manufacturing of articles by electron beam fabrication processes is identified at col. 12, lines 8-15 in U.S. Pat. No. 7,168,935 (incorporated by reference). In Seufzer and Taminger, “Control of Space-based electron Beam Free Form Fabrication” (accessed at ntrs.nasa.gov/archive/nasa/casi.ntrs.nase.gov/20070030308—2007030399.pdf) (incorporated by reference), the authors address a possible approach to a closed-loop control system. See also, Sharma, “On Electron Beam Additive Manufacturing Process for Titanium Alloys” (Abstract for Session on Apr. 27, 2009 Spring 2009 AIChE National Meeting) (incorporated by reference).
U.S. Pat. No. 6,091,444 (incorporated by reference) elaborates on some of the difficulties faced in imaging high temperature melts. The patent illustrates an example of a high temperature melt view camera that includes a water cooled enclosure with a pinhole in it, through which a gas is passed. An example of an electron image detector configuration is illustrated in U.S. Pat. No. 4,794,259 (incorporated by reference).
Until the present invention, notwithstanding efforts by others, the above-described needs for improvements in LM systems have remained unmet.